The fuel system is designed to provide an uninterrupted fl ow
of clean fuel from the fuel tank to the engine. See Chapter
3, Components and Systems, for more information on fuel
tanks. See earlier section in this chapter for specifi cs on fuel injection systems. The fuel must be available to the engine
under all conditions of engine power, altitude, attitude, and
during all approved fl ight maneuvers. [Figure 4-17]

Fuel Pumps

WSC aircraft with carburetors have engine-driven fuel pump
systems. A diaphragm pump is the primary pump in the fuel
system for two-stroke engines. Air pulses in the crankcase
actuate a diaphragm and provide fuel under pressure to the
carburetor. Four-stroke engines have a mechanical pump
driven directly off the engine.

Sometimes an electric auxiliary pump is provided for use in
engine starting and in the event the engine pump fails. The
auxiliary pump, also known as a boost pump, provides added
reliability to the fuel system. The electric auxiliary pump is
controlled by a switch in the fl ight deck.